In this study, a calibration setup for laser beam positioning systems used in visual inspection applications in industry is designed and manufactured. The laser positioning systems generate movable parallel laser lines on the projection surface. There are several translational and angular error sources affecting the positioning accuracy of the laser lines on the projection surface. Especially, since the laser line positioning error caused by angular error sources increases with the distance between the laser system and the projection surface, angular parameters of the laser sources should be measured and adjusted precisely. The calibration setup developed in this study detects the laser line positions at two different projection distances by means of laser sensing cameras which are positioned precisely along the laser lines and laser positioning axis which is perpendicular to these lines. Cameras detect the positions of the laser lines which are directed to the camera sensors with micrometer repeatability by means of some special imaging algorithms. The precise positioning of the cameras requires a special camera positioning system. For this reason, the disturbances like temperature changes and vibration should be minimized. In order to provide a suitable environment for the calibration system, special tests are conducted and a special calibration room is constituted. Construction inside the room is also made by considering the required ambient parameters. Finally, several verification tests of the calibration system are conducted.

In order to understand how does the intense laser interact with matter we first of all study the ionization process. In this highly nonlinear region the conventional perturbation theory will fail to predict the experimental results. Alternative theories have been proposed in the past few decades. The fundamental difficulty in these new approaches is when laser field becomes so intense such that it is comparable to the Coulomb field at where the ground state electron mainly concentrate, we have to treat the laser field and the Coulomb field on an equal footing. The analytical solution that can describe the propagation of electron in both the laser field and the Coulomb field has not been found; therefore, in these new theories the ionization process is either divided temporarily into laser period and Coulomb period or spatially into laser field domain and Coulomb field domain. The propagation of electron in the full Hamiltonian is avoided.

In order to understand how does the intense laser interact with matter we first of all study the ionization process. In this highly nonlinear region the conventional perturbation theory will fail to predict the experimental results. Alternative theories have been proposed in the past few decades. The fundamental difficulty in these new approaches is when laser field becomes so intense such that it is comparable to the Coulomb field at where the ground state electron mainly concentrate, we have to treat the laser field and the Coulomb field on an equal footing. The analytical solution that can describe the propagation of electron in both the laser field and the Coulomb field has not been found; therefore, in these new theories the ionization process is either divided temporarily into laser period and Coulomb period or spatially into laser field domain and Coulomb field domain. The propagation of electron in the full Hamiltonian is avoided.

A novel method of simulating edge-emitting semiconductor lasers in a non-equilibrium steady-state is developed. The simulation is based on a non-equilibrium Green's function (NEGF) method. The Dyson equation (central equation of this method) is derived and written in a basis suitable for numerical implementation. The electron-photon self-energy is derived form scratch for the case of the edge-emitting laser. Other interactions present in the simulation are phenomenological scattering and scattering due to longitudinal optical phonons. This microscopic approach significantly reduce the number of phenomenological parameters needed to simulate laser. As an example, the theory is applied to analyze quantum well laser with the effective mass Hamiltonian. The major laser characteristics such as modal gain, threshold gain, carrier and current densities are determined.

In recent and upcoming years new lasers are being constructed withever higher intensity. These lasers open up the possibility of probingthe high intensity regime of particle physics, which will lead to etherconrming our current models in this regime or the discovery of beyondstandard model physics. However most previous theoretical results in thisarea are based old assumptions about the intensity and shape of the laserpulse that are no longer valid. In this thesis we calculate the tree-levelprobabilities for multi photon emission from an electron propagating inan arbitrary plane wave electromagnetic eld. We show that the classicallimit of our result agrees with the purely classical description of the sameevent. We calculate the soft emission correction to non-linear Comptonscattering. We conclude that our results are infrared divergent and arguethat this will be solved by including loop contributions to the process. Ourresults provide an important component for the theoretical predictions forthe outcome of scattering experiments in high intensity background eld.This thesis will add to the understanding of high intensity QED.

Interferometry and holography are two well-known methods for measuring distances, positions, vibrations, index of refraction etc. In these methods a coherent light source is used to create interference between different parts of the light. Since the wavelength of the light is used as reference it is possible to achieve very good accuracy in the measurements. The need of small and cheap light sources for these applications is large and an interesting alternative would be to use ordinary semiconductor diode lasers. These are unfortunately not designed to give sufficiently good coherence. In this Master Thesis work investigations of how the coherence of semiconductor diode lasers is affected by changes in temperature, injection current and between different individuals are performed. A Michelson interferometer is used to create an interference pattern where the contrast then can be analyzed. The contrast is related to the coherence of the laser, i.e., good coherence will give high contrast. The results show that in order to drive the laser in a stable way it is better to hold the temperature constant and varying the injection current until the wanted output power is achieved instead of doing the opposite. The results also indicate that the best coherence is achieved for low temperatures (around 10 OC) and high injection currents (around 80 mA). During these conditions a contrast of 70 % -80 % is achieved. The result of this Master Thesis work gives a hint on how to run a semiconductor diode laser in a stable way.

With the escalating demands for optical communication network system, the need for broadband gain medium in optical communication has increased. Among them, Cr4+:YAG crystal has shown an exceptionally successful broadband amplified spontaneous emission (ASE) light source that fully cover 1.2-1.6 £gm range (3-dB bandwidth up to 265 nm). More recently, we demonstrated the realization of a waveguiding, low-loss, and low-threshold Cr4+:YAG double-clad crystal fiber (DCF) based ultra-broadband ASE light source, optical amplifier, and laser grown by the co-drawing laser-heated pedestal growth technique. These results demonstrate the potential of the Cr4+:YAG DCF for the replacement of the erbium doped fiber in future optical communications. To further improve the efficiency of Cr4+:YAG DCF based active devices, here we show the difference in thermal expansion coefficients between a YAG core and an inner cladding creates a significant localized strain field by near-field scanning optical microscope (NSOM), which can result in optical confinement and provide the possibility to simultaneously alter the Cr3+ and Cr4+ fluorescence lifetime with varied core dimensions. The results indicate that There exists a nearly zero strain across the entire core with a diameter of ~20 £gm, which is beneficial the higher Cr4+ fluorescence lifetime (+6.43%) and emission cross section (+19.17%) as compared with 11-£gm core. In addition, we have successfully investigated the near-field modal characteristics of Cr4+:YAG DCF laser and ASE by NSOM. The results demonstrate that the Cr4+:YAG DCF laser produced nearly a single-mode (LP01) output with diffraction-limited beam quality of M2 ~1.1; for ASE, the modal weighting of LP01 decreases from 26% to 15% as the number of modes increases from 4 to 7. The results offer a guideline not only for further fabricating Cr4+:YAG DCF tunable lasers, but for efficiently coupling a broadband ASE light source into a single-mode fiber.

The purpose of this thesis is to fabricate the In0.75Ga0.25As quantum dot (QD) lasers, and analyze the optical properties of laser devices to be applied to optical fiber communication systems. In laser materials, we grew 12-layer In0.75Ga0.25As QD strcutures by molecular-beam epitaxy (MBE) with S-K mode on GaAs substrate, which contains the cladding layer material Al0.5Ga0.5As (C433) Al0.25Ga0.75As (C486) and Al0.2Ga0.8As (C485) of the three structures, the emission wavelength of about 1.3£gm. In the waveguide design, the design of 2.2£gm ridge width waveguide, the purpose is to enable the single transmission mode in the waveguide, so that smaller dispersion losses. Using ridge waveguide and cleaved mirror as the formation of Fabry-Perot cavity laser. In the quantum dot laser characteristic, C485 in the cavity length is 3000£gm of threshold current is 80mA with a slope efficiency of 41.88mW/A, the main emission Peak at 1201nm, the second Peak at 1197nm, the third Peak at 1182nm ; however C486 cavity length is 3300£gm of threshold current is 120mA with a slope efficiency of 27.44mW/A, the main emission Peak at 1215nm, the second Peak at 1205nm. C485 of the threshold current density is 1212 A/cm2, C486 of the threshold current density is 1454 A/cm2.

There are several advantages for optical communication in free space such as simplification,convenience, high bit rate,and sasy design,Free-space optical communication is an alternative for short distance communication. In this work, we desighn and fabricate the optical transmitter and receiver for delivery of audio signal in free-space communication. In circuit design section, audio signals proceed to analog to digital conversion (A/D)and then encode the data. The procedures of encoding block include parallel-series conversion, data cell process adding starter and stop bit, thereby modulate the laser by PCM format in free space. Data cell at receiver terminal will be decoded exactly and synchronized with transmitter terminal for data transmission. After digital to analog conversion, parallel-series data will decode to audio signals. We have accomplished the circuit design of optical transmitter and receiver for transmission of audio signals. Transmission bit rate, optical output power, and transmission distance at transmitter terminal are 200kbit/s,15mW,and >50m, respectively.

ABSTRACT A DIP (dual-in-line) laser diode module packaging by soldering technique was investigated. We made high coupling efficiency fiber lens under the best arc fusing conditions. The coupling efficiency of fiber lens was obtained 82%, while offset of fiber lens center was less than 0.5mm and curvature radius was about 9mm. We metallized the high coupling efficiency fiber lens, and packaged it in the DIP housing. The components inside the module were uncoated FP (Fabry-Perot) laser chip, p-i-n detector, substrate, and cooler. We made a package process as follows: 1) We utilized the heating apparatus to fix the FP laser, PIN detector, and thermistor on the substrate. 2) We utilized the heating apparatus to make the cooler fixed on the DIP housing and the substrate fixed on the cooler. 3) We utilized the electrothermal heating machine to melt 1.5mm3 indium wire and adjusted the fiber lens by tweezer to couple light into the fiber inside the DIP housing. We obtained the 2.93mW output power and 58.6% coupling efficiency after packaging. The post-soldering-shift resulted from the indium solidification was the most important factor affecting the coupling efficiency. By improving substrate design properly, we could reduce the indium quantity to minimize the solidification effect. The post-soldering-shift should be controlled below 1mm in the transverse axis and below 10 mm in the longitudinal axis, respectively. Finally, We achieved an external cavity fiber grating laser module with 2mW output power, and got an open eye pattern after measuring the DIP transmitter module.